sodium; magnesium bromide in tetrahydrofuran to a suspn. of active Mg prepd. by redn. of MgBr with Na in boiling THFis added 2,3-dimethylbutadiene, stirred for 3 d at 25°C, 1-chloro-1-ethoxy-1-germacyclopent-3-ene is added dropwise, stirred for 12 h at25°C, refluxed for 24 h; hydrolysis, distn.; elem. anal.;